This invention relates to an electromagnetic coupling device comprising a yoke assembly in which the ends of an exciting coil are electrically connected to the terminals of a connector held by a yoke.
An electromagnetic coupling device in the prior art, particularly an electromagnetic clutch which is installed on the compressor of an air conditioning system for an automobile and which is used as a power transmission device, has a structure wherein the terminal housing of a coil side connector, connected with a power source side connector, is held by a yoke and wherein a pair of terminals embedded in the terminal housing are electrically connected to the ends of an exciting coil.
The yoke assembly of an electromagnetic clutch proposed in the official gazettes of Japanese Patent Applications Laid-open No. 127662/1995 and No. 127663/1995 (hereinbelow, termed the "preceding invention") comprises a yoke including a coil bobbin around which an exciting coil coated with an insulating film is wound, an annular groove in which the coil bobbin is snugly fitted, and through holes into which projections provided on a flange lying on one side of the coil bobbin are inserted; a pair of terminals which are inserted from outside into the through holes of the yoke and whose distal ends are pressedly fitted on the projections of the coil bobbin; caulking pieces with which the respective terminals are integrally formed and to which the initial winding end and terminal winding end of the exciting coil are respectively fixed by caulking; a casting resin which is poured into the annular groove of the yoke so as to insulate the exciting coil from the exterior; and the terminal housing of a coil side connector which is formed of the casting resin. Incidentally, the bent caulking pieces of the terminals and the corresponding ends of the exciting coil are electrically connected in such a way that the coating film of the exciting coil is perfectly torn off owing to heat generated by the exciting coil energized.
In addition, a diode package which functions as a surge voltage absorbing device is assembled in the terminal housing of the yoke assembly. The diode package is constructed as a separate component lest a diode should damage under heat and pressure when the terminal housing is molded with the casting resin. Further, the diode package has a structure including a concavity in which the case of the diode is accommodated, a pair of through holes into which the pair of terminals are individually inserted, and a guide portion which is extended outside and which is engaged with a recess formed in the terminal housing of a power source side connector. Herein, the pair of leads of the diode are individually projected into the through holes. In addition, while the respective terminals are being inserted into the through holes of the diode package, this diode package is snugly fitted into the terminal housing, whereby the respective terminals and the corresponding leads of the diode are electrically connected.
With the yoke assembly of the preceding invention, the terminal housing is integrally molded using the casting resin of the exciting coil, and hence, the pair of terminals are previously fixed to the projections formed on the flange of the coil bobbin. Besides, the initial winding end and terminal winding end of the exciting coil are led out of the through holes of the yoke, and the caulking pieces of the respective terminals disposed outside the yoke are caulked, thereby to electrically connect the ends of the exciting coil and the terminals. In the electromagnetic clutch which is installed on the compressor, the yoke assembly is constructed between a rotor, which is supported through a bearing around a cylindrical portion provided on the front housing of the compressor, and the side surface of the front housing of the compressor. Accordingly, the development of a yoke assembly in which the quantity of protrusion of the terminal housing is small is desired in order that the full length dimension of the compressor on which the electromagnetic clutch is installed may be prevented from enlarging.
Accordingly, one object of this invention is to provide an electromagnetic coupling device comprising a yoke assembly in which the quantity of protrusion of a terminal housing is small. Additional objects of this invention will be apparent from the discussion below.